Yell accused Yellowikis co-founders Paul Youlten and his 15 year-old daughter Rosa Blaus of "misrepresentation", "passing off" and suggested that using the name Yellowikis could "constitute an 'instrument of fraud'." Passing off is defined as misrepresenting a product and passing it off as one's own. Passing off is a form of trademark infringement.

Yell is demanding that Paul and Rosa close down the website, transfer the domain names to Yell and agree to pay damages to Yell for loss of profits. Yell made $2.4bn in 2005, whereas Yellowikis had a loss of $500. The $500 was used to print T-shirts promoting Yellowikis at the Wikimania conference in Frankfurt.

Paul Youlten said: "This threat from Yell to shut us down looks like a sign of desperation. The whole yellow pages industry is in crisis. Use of the paper directories is collapsing as people get broadband Internet connections in their homes. Small and medium sized businesses are beginning to notice that their customers are ringing them up and saying 'I found you on Google' and not 'I found you in the yellow pages'."

Rosa Blaus said: "Maybe they are a bit jealous of Yellowikis because we allow companies to add videos, skype IDs, email addresses, instant messaging, in as many categories and languages as they like for free." Blaus suggested to her father that they set up Yellowikis after she noticed small businesses were deleted from Wikipedia for not being "encyclopaedic".

Yellowikis has been growing at 8.7% month-on-month and has 494 editors and about 5,000 articles listed.

The threat of legal action came after an article published in The Independent newspaper mentioned Yellowikis.